Apparatus for picture transmission or the like



March 21, 1933. Q, FULTON 1,902,552

APPA-RATUS FOR PICTURE TRANSMISSION on rm. LIKE I Filed March .16, 1929.-

mumlllllll I ture.

Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE OTHO FULTON; OF BROMLEY, ENGLAND APPARATUS FOR PICTURE TRANSMISSION OR THE LIKE Application filed latch 16, 1929, Serial No. 347,628, and in Austria August 22,

I This invention is concerned with improvements in or relating to methods of and apparatus for picture transmission, television or the like. v

In known systems for the transmission of pictures or the like employing a receiver of the kind comprising a recording apparatus that is not properly responsive to picture signals varying in amplitude according to the light and shade of the transmitted picture, the reproduction of half tons pictures cannot be obtained Without the introduction of complicated measures including the use of screens. For example, a simple receiver operating in the well known manner b electro-chemical reaction is not proper y responsive to such varying picture signals.

An object of the invention is to provide a method of transmitting pictures or the like, and apparatus therefor by means of which a picture can be transmitted in such a manner as to be reproduced b the receiver of the aforesaid kind asa ha f-tone reproduc tion.

The presentinvention comprises a method of picture transmission, television or the like employing a receiver of the kind aforesaid wherein the energy fluctuations produced or controlled by an exploring device (e. g. a light sensitive cell) and varying in amplitude in accordance with the light and shade of the picture, are translated into signal impulses of differing time duration according to the natureof the picture.

5 The invention also comprises a method as aforesaid wherein the energy fluctuations are applied to an electrical system which is periodically reduced to a neutral state and l is brought to an active state by the energy 49 fluctuations for a greater or'lesser time interval according to the nature of the pic- The method of this invention maybe carried out by charging an electric condenser at 4 uniform intervals and controlling the discharge of the condenser by means of the energy fluctuations aforesaid to produce signal impulses of difl'ering time duration acv cording to the variations of amplitude of the energy fluctuations.

Thus by exploring the picture to be transmitted with a device such as a photo-electric-cell which is influenced for example as regards its electrical resistance in proportion to the light beam directed upon it and using the device as a discharge path forthccondenser, the discharge period will vary in duration according to the intensity of the lightupon the photo-electric-cell, By applying the potential variations produced at the condenser to the control electrode of a thermionic valve, impulses can be obtained which have a duration depending upon the time of discharge.

The condenser 1s charged at uniform intervals so that a succession of signal impulses is obtained.

The invention will now be more particu larly described with reference to the accompanying drawing, in which:

Figure 1 is a diagrammatic representation of means for carrying out the invention;

Figure 2 shows diagrammatically an arrangement of apparatus in a practical form;- and 7 Figure 3 shows explanatory charge and discharge curves. I

Referring to Figure 1 a photo-electric cell 11 is connected across the grid and cathode of a three electrode thermionic valve 12 and to the grid of the valve there is also connected a brush 13 bearing upon a rotary switch member 14 having contacts which are connected to the negative terminal of a battery 15 thefpositive terminal of which is connected to ,the cathode of the valve.

The switch member 14 is rotated and the grid'of the valve 12 and one element of the cell 11 will consequently be givena negative charge from the battery 15 at regular intervals, namely, when a contact of the switch member 14 'passes beneath the brush 13.

The picture to be transmitted is explored by a beam of light directed from the picture on to the cell 11 and this beam therefore varies in brightness according to the light and'shade of the ictureu When there is substantially no lig t directed onto the cell corresponding to a very dark part of the picture no current will flow in the anode I I circuitof thevalve 12 owing to the negative tained through along the line 20,

charge upon the grid thereof.

When a bright beam of light is directed upon the cell corresponding to a light art of the picture the cell will become con uctive so that the negative charge upon the grid rapidly leaks away through the cell and a current will flow 1n the anode circuit of the-valve. I

By suitable selection of the electrical values of the several components the ap aratus can be adjusted in such manner t at when no light is directed upon the cell voltage from the grid will not rise Suficiently to enable a current to appear in the anode circuit of the valve (or the anode current to be increased) within the interval between two successive negativecharges obthe switch 13, 14. Thus, as the resistance of the cell will be decreased in proportion to rent. impulses obtained in the anode circuit of the valve are proportional as regards their duration to the brightness of the light upon the cell.

In Figure 3 the time intervals are plotted along the line 20, 21, the grid 22, and 23, 24 represent at which the valve be the grid potential The intervals between comes conductive. the negative charges upon cated by 125. I I If it is assumed that the voltage upon the grid on being charged immediately reaches the value indicated at 20 the subsequent discharge which takes place through the cell in accordance with the. general known exponential function is represente by the curve such as 26, and this is repea for each charge. The shape of the curve depends upon the brightness of the li ht beam that is directed upon the cell 11, t at is to say upon the resistance through which the charge leaks awa In Fi re 3several typical curves are shown or the rise of the potential on the grid for different resistance values assumed by the cel Thus the curve 25 may represent an intense illumination of the cell. The curve 27 corresponds to a less bright illumination and the curve 28 for no illumination shows the voltage rising insufliciently to cause a current to appear in the anode circuit of the valve.

Therefore,

assuming an illumination of the cell corresponding to the curve 26, 1m-

additional apparatus for pulses are obtained which havethe form of the shaded portions in Figure 3 which vary in duration according to the brightness of the picture being e lored." These sigupon the queue of charging the grid'of the valve.

Re erring to Figure 2, there .is shown the practical the light upon it the cur potentials the grid are indiof current uced with uniform smooth and pleasing appearance of the reroduced icture. A

Althoug the charging of the light sensitive cell and associated parts at uniform intervals is efiected in the example described by means of a rotary switch which may for example be self excited or driven in any suitable manner, any other means may be employed for supplying 'the charging potentials such as purely electrical means.

The interval of time between successive char es is preferably chose in such a manner t at havin regard for he circumferential speed. of t e transmitting-or receiving.

A battery I a resistance 32 is drum the reproduced picture hasa screen effect which isof the usually employed in rinting. By adjusting the frequency 0 charging and by a roper selection of the electrical values of the apparatus em loyed it is possible to obtain any desire degree of fineness and by suitable adjustment the gradation of the picture can influenced in order to flatten or intensify the reproduction of a picture that is not very suitable as regards contrasting values.

I claim: u

1. In a communication system, .a threeelectrode valve having a grid and a cathode, a condenser connected incircuit with said grid and cathode, means for periodically charging the condenser to interrupt the flow from said valve, and a photocell provide a leak path interruption of the same 01 connected to the grid to whereby the period of flow of current from proportional to the intensity of the illumination impinging 'upon said cell.-

der as that the valve is inversely 2. In a communication system, the combi- 1 nation with a three-electrode valve having an anode, a grid, and a cathode, a photocell connected to said grid to provide a leak path, and mean for periodically charging said grid to preclude the flow of current from said anode until the grid chargeleaks ofi through said I v In' testimony w ereof I afiix my signature.

OTHO FULTON 

